1. Field of the Invention
The present invention relates to a valve timing adjuster that adjusts timing of opening and closing at least one of an intake valve and an exhaust valve of an internal combustion engine (hereinafter referred to as an “engine”).
2. Description of Related Art
A conventional hydraulic valve timing adjuster is known to adjust timing of opening and closing an intake valve or an exhaust valve of an engine in a following manner. The valve timing adjuster is known to have a regulating member that is fittable with both of a vane rotor and a housing such that rotation of the vane rotor relative to the housing is regulated when oil pressure is not supplied to the adjuster during the engine start. In the valve timing adjuster, by fitting the regulating member with the housing, a phase difference between the vane rotor and the housing (or in other words, a phase difference between a driven shaft and a drive shaft) is maintained at a certain phase difference that enables the engine to start. Normally, before the engine is stopped, the vane rotor is rotated to a position for fitting the regulating member with the housing. As a result, the regulating member is reliably fitted with the housing, and thereby the vane rotor and the housing are positioned to be ready for the engine start in the next operation.
However, in case of a sudden stop of the engine, such as a case of an engine stall, the regulating member is positioned out of the fitting bore of the housing. In other words, in case of the sudden engine stop, the phase difference between the driven shaft and the drive shaft may indicate a state that is not appropriate for the engine start. In the above condition, during the next engine start, the engine may not be started. In order to address the above failure in restarting the engine, there is proposed a certain valve timing adjuster. In the above adjuster, an intermediate position or an advance side is set as a fitting phase, at which the vane rotor is fittable with the regulating member. Also, a return spring is provided for urging the vane rotor in the advance direction. As a result, when the engine suddenly erroneously stops, the urging torque of the return spring rotates the vane rotor to the fitting phase.
However, in the attempt to restart the engine, the urging torque of the return spring may not be able to move the vane rotor to the fitting phase, and thereby it may be impossible to start the engine disadvantageously. The reason of the above disadvantage will be described below. Typically, during the restarting of the engine, a starter motor is used for the cranking of the engine, and the rotational speed of the engine (drive shaft) may be normally about 100 to 500 rpm. In the above slow rotation operation, because of “the increase of a contact pressure at each slide part” or “difficulty in sufficiently maintaining oil film”, the average cam torque, which includes the friction of valve system, may increase to be greater than the urging torque of the return spring. As a result, the urging torque of the return spring may not be able to successfully move the vane rotor to the fitting phase disadvantageously.
In order to address the above disadvantages, a valve timing adjuster described in JP-A-2003-214123 has a mechanism (retard rotation regulating mechanism). At the time of the engine stall, the retard rotation regulating mechanism regulates the rotation of the vane rotor within a certain phase range, in which the vane rotor is fittable with the regulating member, and the retard rotation regulating mechanism prevents the vane rotor from rotating further in the retard direction over the certain phase range. However, the retard rotation regulating mechanism of the valve timing adjuster of JP-A-2003-214123 has a complex configuration, and thereby manufacturing cost of the adjuster is increased disadvantageously.